In reproduction methods for printing a color proof is usually made, for example, from a slide using corresponding color filters. The color space associated with a scanner is an RGB color space with the process colors red (R), green (G) and blue (B). During the printing, for example, offset printing, the color proofs are screened. The color impression in offset printing is based on autotypical color synthesis, i.e., on a combination of additive color synthesis and subtractive color synthesis. The process color space of the printing inks is usually a CMYK color space in which the process colors are cyan (C), magenta (M), yellow (Y) and black (K).
The resulting print should naturally be as close as possible to the original, i.e., the quality and color fidelity of the image reproduction in the print should be as high as possible.
During the printing itself, a specific problem occurs in that mechanical influences cause ink dots to be squeezed, for example, in offset printing during transfer from the offset plate to the rubber blanket and then again during transfer from the rubber blanket to paper. A printed screen dot is then enlarged during the printing operation, i.e., it has a larger dot area than was actually provided for by the transformation from the original to the data required for printing. In principle, dot gain is an undesired and annoying effect which may affect the color reproduction in the print. The effect of dot gain may result in color distortions in the print in comparison with the original.
The effect of dot gain is indicated by a so-called characteristic curve of printing (printing characteristics) in which the area coverage in the print is shown with respect to the area coverage in an original with a colored application, for example, a film or a plate. Without dot gain, the characteristic curve of printing would be a straight line which represents a line bisecting the angle between ordinate (area coverage in the print) and abscissa (area coverage in the original with a colored application).
In the publication “PHILOSOPHIE DES COLOR MANAGEMENT; Postscriptum Color Management” by S. Brües, L. May and D. Fuchs, LOGO GmbH, 2nd edition, February 2000, reproduction processes are described against the background of color management.
The object underlying the invention is to provide a reproduction method for printing in which the dot gain is controllable so as to obtain optimum reproduction results in the print.